Dynamic ligament balancing system

ABSTRACT

A method and system for measuring tension, pressure, and distance of knee tissue, the system comprising a prosthetic inlay device comprising at least two platform structures, wherein each of the platforms are supported on a scissor arm structure and a coil spring, a force sensing sensor configured beneath each coil spring, and a connector cable coupled to the force sensing sensors.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains material,which is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of PCT/AT2016/000043, entitled“DYNAMIC LIGAMENT BALANCING SYSTEM (DLB),” filed on Apr. 28, 2016, thedisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

This application generally relates to soft tissue testing systems, andin particular, apparatus and methods for measuring tension, pressure anddistance in the soft tissue of a patient's knee in connection withendoprosthetic surgery.

Description of the Related Art

The knee is very stable and can reach up to one and a half short-termton load, and it is a commonly injured joint for athletes. However, kneeproblems can occur at almost all ages even if injury though sports areavoided. In addition to acute damage due to sports-related overloadssuch as ligament tears, meniscus injuries, or knee-disk dislocations,may also occur. Risk factors such as overweight, congenital or acquiredpostural impairment, also untreated injuries of the knee in addition tothe natural aging process can contribute to knee joint damage. Smallerinjuries in the joint may be severe enough to cause medium to long termjoint damage when they are not treated properly or at all.

In the case of advanced knee joint wear, knee joint arthrosis, theinsertion of an implant may be a final step that can be taken bypatients as a solution for the permanent relief of his pain to restorejoint function and improvement of mobility. To restore the patient to ahealthy and active lifestyle, it is necessary by means of endoprostheticsurgery, to use an artificial knee joint prosthesis. Endoprosthesis is asurgical procedure, in which permanent implants remain in the body thatcompletely or partially replace the damaged joint. The procedure isgenerally considered safe, but only if it is carried out by experiencedspecialists. The prospect of alleviating pain and more life-joy andquality of life for the patient is therefore very sensitive to thesurgeon's experience.

When asked how the quality of life has changed after surgery, 14% ofpatients answered with negative or very negative, and only less than 80%are satisfied with the result of the operation or very satisfied. Thereason is mainly the lack of standardization and standardization of thefabrication of tendon and tendon tension in the patient. Surgery cancause pain in the patient by incorrectly adjusted soft tensile stressesdue to loosely or tightly adjusted tendons, which are equally unpleasantand stressful for the patient. These patients are often mistreated formany years and often a final remedy is another surgery, where the causeof the pain, the wrong compliance of the soft tissue stress iseliminated. Doctors are constantly confronted with such cases in theirpractices and has therefore dealt extensively with the idea of how theendoprosthetics in the area of the knee can be simplified in that thepatient can be replaced in a standardized surgical method where a longprocess of suffering with a new operation is spared, long convalescencetimes are avoided and patients briefly after surgery can again live anactive and healthy lifestyle with high quality of life and joy of life.

The knee joint is the largest joint in the human body and connects thethigh bones, knee, and shin bone. As so-called twist and hinge gels,allows diffraction and bending stretching the leg, as well as a slightturning in and out in the flexed state. The knee joint is secured andstabilized by complex system of ligaments, in cooperation with thefunction of tendons, muscles connective tissue, the articular cartilageand the intervertebral discs, the menisci. The knee must be able towithstand heavy loads during its daily use and also guarantee sufficientmobility. The contact surfaces of the knee joint bones are severalmillimeters thick, very smooth and elastic cartilage layer. Cartilagecells and matrix tissue function as a shock absorber and allows for apainless and undisturbed mobility of the knee joint. The two menisci,which consist of connective tissue and elastic cartilage and extendingbetween the femur and the rail header, enlarge the joint surface of theknee and thus distributing the pressure or the weight on the jointoptimally affects that overall knee. The joint is encapsulated by acapsule, which is used for the nutrition of the articular cartilage.

Endoprosthetics has made great strides in the past two years, thereforea large number is now available as a replacement for damaged joints.Prosthesis models are made by different manufacturers but are generallycomprised of three main components—a femoral part also called a femoralpart, a lower leg part of the tibial part, and knee arthroplasty orpatellar replacement. The femoral part and the lower part are made of achromium, cobalt, molybdenum metal alloy or different metal alloys, andthe knee portion consists of the plastic polyethylene. The choice of theappropriate type of prosthesis for the patient depends on thequality—the knee-deep bones, the stability of the sidebands, and theaxial deformity of the knee joint (X, O-legs).

There are two types of prosthesis which can be used. A prosthesis forsurface replacement, and a second type, a steered axle endoprosthesis.Surface replacement can be used when there is sufficient bone strengthand a stable sideband. This type offers the advantage of minimal boneloss. The stability of the artificial joint is determined mainly by theintact and stable sidebands. The upper part of the thigh has the shapeof a shell which fits the right fit thigh roller and is placed after ithas been form-fitted. The tibial part has the form of a plate, which isconnected to a stem. This plate is placed on the previously preparedlower leg plateau. The stem optimizes the connection between the implantand the lower margin mark. On this, an inlay made of anabrasion—resistant plastic is placed, which has an inlay of theartificial thigh replacement corresponding to a concave depression asthe actual joint surface. Patellar replacement is performed by replacingthe back surface of the knee disc with a plastic disc.

Axle-guided endoprosthesis may be used for soft bones, loose side bandsor shear axis deformities. The axis-guided prosthesis is implanted. Indoing so, more bones have to be sacrificed, but the artificial jointoffers a very high stability, the reduced function of the loosenedsidebands compensated. Again, femur and tibia are appropriately preparedso that the individual prosthesis parts fit into the seat. The anchoringof the prosthesis parts is achieved by means of the long stems, whichallow an extremely stable attachment. The stability itself is achievedby a hinge joint present in the prosthesis. For each part of theprosthesis, whether it is a surface replacement or a guidedendoprosthesis, they are available in different sizes, all of which arecompatible with each other. Due to this modular design of theprostheses, it is possible to intraoperatively compensate for thedimensions of the patient's personal knee joint.

In order to replace the diseased knee joint with an implant, the surgeonmakes a curved skin incision that is approximately 20 cm long at thefront of the joint. The joint capsule is then opened. The knee joint isangled about 90° and the anterior cruciate ligament and the remains ofinternal and external ligaments and external meniscus can be removed.Subsequently, the thigh, then the lower plateau, and finally the kneearthroplasty surface is prepared by exactly predetermined bone sections,such that the prosthesis not only comes to an optimal seat, but alsoleads to a sufficient degree of movement for the patient. Afterinsertion of the three prosthesis parts, with or without cement, plasticinlays, the joint is implanted and flexibility is tested. During theoperation, it is ensured that not only the normal leg axis is restored,but also that the leg is fully stretched and over a right angle. This isnecessary especially for everyday movements such as climbing stairs.

For performing the surgery and placing the implants correctly, differenttools and gauges from the individual implant manufacturers areavailable, which provide a precise resection of the bone and an exactpositioning of the implants. However, a measuring instrument or aprecision tool for recording the values of the soft tissue tension (theligament balancing) of the patient before surgery, and for adjusting thesoft tissue tension during the operation, in order to verify anddocument the values after completion of the procedure, does notcurrently exist. Existing instruments in the area of endoprosthetics ofthe knee are only on the maintenance of the articular line but not thepreservation of the joint line tension in the soft tissues. The softtissue tension is still adjusted by means of a “simple clamping tool”and is dependent on the experience of the surgeon. Decisions for themaintenance of the correct tension condition after the intervention isat the subjective assessment of the surgeon, which is very sensitivewith experience in carrying out such interventions, and is not linked toobjective evaluation criteria. If this soft tissue tension is applied bythe surgeon on the basis of a false judgment (e.g., is too tight, or tooloose), this has a dramatic negative-effect impact on the patient'swell-being.

Before the operation, the patient was greatly restricted in movement dueto the severe wear of the cartilage and the missing damping function inthe knee. With surgery, pain in the joints may have disappeared, but maynow experience new pain in the region of the muscles and the tendonmuscles. Inaccurate implantation results in the new pain in the sense ofan overloading of the muscles, negatively influencing the success of theoperation. As a result, the mobility as well as the quality of life ofpatients can be severely hampered. The resulting increased need fortherapies and drug administration causes considerable additional costsin the health care sector, which are avoidable. The consequences areoften lengthy and expensive after treatments of the patient, such as,for example, different movement therapies, pain therapies (as potent asmorphine patches) and are all too often long periods of suffering forthe patient.

The remedy is, however, only a new intervention on the already operatedknee to correct the previous error. In summary, the patient experiencesa long process and painful suffering if the operation is poor.Unsatisfactory operation results also causes the insurer enormous extracosts. Accordingly, there is a need for an objective measuring andcontrol system for the reproduction of the original muscle and tendontension during the implantation of the knee implant of the patient.

Stryker Medical is a global group with more than 26,000 employees withits product range is mainly focused on the development and distributionof medical and orthopedic articles in the field of endoprosthetics, thetraumatology and endoscopy. Stryker Medical distributes a softwareproduct under the name OrthoMap that provides automatic dimensioning andpositioning of the implants on the basis of the unique anatomy of thepatient. The software solution is primarily aimed at the mechanical axisof the patient.

Corin Group PLC, headquartered in England, develops and manufacturesworldwide, products in the field of endoprosthesis hip, knee, and anklejoints. Corin draws on many years of experience in the field ofbone-conservation and gentle implant technology. The Corin implants arecharacterized by their optimized longevity, significant abrasionreduction and reduction of the contact stress of knee implants comparedto “single radius designs” from other manufacturers. The designadditionally takes anthropometric female and male features based onglobal data to ensure optimized performance in implant seating. Aninstrument offered by Corin in combination with the design of theImplant—Unity™ provides intro-operative flexibility. Stems andaugmentations, in the case of primarily complicated interventions ismade possible by means of the instrument. Here, as with Stryker, themain focus is on preserving the joint line.

As is also the case with the two competitors above, Zimmer Biomet has acomprehensive portfolio of innovative knee products and instruments.Their instrument portfolio includes a tool for optimum axial alignmentand the alignment of the implants, however a tool for measuring the softtissue tension of the patient before implant placement and adjustment ofthe optimal soft tissue tension before fixation of the implant iscompletely absent.

A system for measuring and restoring the soft tissue tension in the legof the patient is neither present nor thought of. Searches for furtherlarge implant and instrument manufacturers in the field ofendoprosthesis, as well as in the examples given above companies, hasprovided neither a corresponding tool to the objective measurement ofthe soft tissue tension, nor the reproduction of this soft tissuetension after the insertion of the implant, has been developed. Inaddition, manufacturers are striving only to sell their own products,therefore mainly instruments and devices that are only offered inconnection with their own implants. These instruments are usually notcombined or can be used with products from other companies.

In summary, therefore, it can be stated that there is a need for amedical tool in the field of endoprosthesis for an objective adjustmentof the dynamic soft tissue tension in the leg of patients during thecourse of the implantation of an artificial knee joint, which is notrelated to any specific implant—it should be platform independent.

SUMMARY OF THE INVENTION

The present invention provides a method and system for measuringtension, pressure and distance of knee tissue. The system comprises aprosthetic inlay device comprising at least two platform structures,wherein each of the platforms are supported on a scissor arm structureand a coil spring, a force sensing sensor configured beneath each coilspring, and a connector cable coupled to the force sensing sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the figures of the accompanying drawingswhich are meant to be exemplary and not limiting, in which likereferences are intended to refer to like or corresponding parts.

FIG. 1 illustrates a prospective view of a ligament balancing toolaccording to an embodiment of the present invention.

FIG. 2 illustrates a right side view of the ligament balancing toolaccording to an embodiment of the present invention.

FIG. 3 illustrates a top view of the ligament balancing tool accordingto an embodiment of the present invention.

FIG. 4 illustrates a left perspective cross-sectional view of theligament balancing tool according to an embodiment of the presentinvention.

FIG. 5 illustrates a left cross-sectional view of the ligament balancingtool according to an embodiment of the present invention.

FIG. 6 and FIG. 7 illustrate schematic top view diagrams of the ligamentbalancing tool according to an embodiment of the present invention.

FIG. 8 illustrates an exemplary user interface for displaying theinitiating of the ligament balancing tool according to an embodiment ofthe present invention.

FIG. 9 and FIG. 10 illustrate an exemplary user interface for recordinga tension profile according to an embodiment of the present invention.

FIG. 11 illustrates a prospective view of a ligament balancing toolaccording to an embodiment of the present invention.

FIG. 12 illustrates a rear side view of the ligament balancing toolaccording to an embodiment of the present invention.

FIG. 13 illustrates a right-side cross-sectional view of the ligamentbalancing tool according to an embodiment of the present invention.

FIG. 14 illustrates a bottom view of the ligament balancing toolaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Subject matter will now be described more fully hereinafter withreference to the accompanying drawings, which form a part hereof, andwhich show, by way of illustration, exemplary embodiments in which theinvention may be practiced. Subject matter may, however, be embodied ina variety of different forms and, therefore, covered or claimed subjectmatter is intended to be construed as not being limited to any exampleembodiments set forth herein; example embodiments are provided merely tobe illustrative. It is to be understood that other embodiments may beutilized and structural changes may be made without departing from thescope of the present invention. Likewise, a reasonably broad scope forclaimed or covered subject matter is intended. Among other things, forexample, subject matter may be embodied as methods, devices, components,or systems. Accordingly, embodiments may, for example, take the form ofhardware, software, firmware or any combination thereof (other thansoftware per se). The following detailed description is, therefore, notintended to be taken in a limiting sense.

Throughout the specification and claims, terms may have nuanced meaningssuggested or implied in context beyond an explicitly stated meaning.Likewise, the phrase “in one embodiment” as used herein does notnecessarily refer to the same embodiment and the phrase “in anotherembodiment” as used herein does not necessarily refer to a differentembodiment. It is intended, for example, that claimed subject matterinclude combinations of exemplary embodiments in whole or in part.

The disclosed systems and methods provide for a platform to helpsurgeons reproduce the natural kinematics of the patient inendoprosthetic surgery. Accordingly, objectives associated with one ormore of the embodiments described in the present disclosure may include:

-   -   Measurement of the soft tissue or tendon tension of the patient        before installation of the implant,    -   Measurement of the joint and rotational angle in connection with        the pressure load on the device,    -   Objectification and standardization of the operating method in        the field of fabrication of the band and soft tissue tension of        the patient during the endoprosthetic surgery,    -   Preparation of the muscle condition of the patient—the original        condition before the surgical procedure,    -   Manufacturer-independent measuring instrument, suitable for all        knee prostheses from different manufacturers,    -   Automatic logging of the measured values, the tension state and        before and after implantation/surgery,    -   Patient-related unalterable protocol to traceability and legal        certainty for critical surgical results for the doctor as well        as the patient, and    -   Easy-to-use measuring instrument.

Through the development of a measuring instrument(s) disclosed herein,for recording the soft tissue tension of the patient in the region ofthe knee before the implantation of the prosthesis and use of thismeasuring instrument for the reproduction of the natural kinematics ofthe patient during and/or after insertion of the implant, arevolutionary step is provided towards an objectification andstandardization of a surgical method during endoprosthetic procedureswith the aid of the measuring instrument. Exact measurements of thetension profile of the soft parts and ligaments of the affected personfor the purposes of comparison during the operation, as well as for thesubsequent complete documentation of the operation results are madepossible with the measuring instrument(s) disclosed herein.

The measurement of the tendon tension itself can take place in contrastto only when preparation of the tibia was previously available. In doingso, the medial and lateral forces during the rolling of the knee (0° to90°) can be captured exactly by the sensors of the disclosed measuringinstrument to record a reference profile produced by tension signalsfrom the measuring instrument. Through the dynamic measurement over theentire movement space, the existing kinematics are measured, the correctincision planes are obtained for the femur in flexion and stretching.This is an approximation, or ideal achievement of the original stateafter the operation ensured.

After successful slices on the femur, measurement of the tendon tensionis repeated with a femur trial and compared with previous measurements.After insertion of the knee implants, before the fixation, presentpractice in the case of the stretching and bending of the joint ismanually and optically checked by the surgeon to determine appropriatefunction, the result for the patient therefore is based on a subjectiveimpression. However, according to embodiments of the present invention,previously recorded values by the measuring instrument can bedynamically compared over the entire radius of movement of the knee.Data from the measuring instrument may be shown on a monitor to show adoctor how far the profile of the tension progress after the finalplacement of the prosthesis in the knee deviates from the previousrecorded reference profile, during the unrolling of the stretched intothe angled state and back again.

In doing so, a user interface may be displayed on the monitor includinga color bar display indicating “in range” and “out of range” values. Thecolor provides a visual depiction of how far the profile deviates fromthe previously recorded reference profile to adjust the implantaccordingly, that the tension profile measured from the device arewithin defined boundaries, and ideally, to show a uniform matching tothe previously recorded reference profile after the setting of theimplant. The comparison of the tension profile may be provided by anapplication that provides a traffic light comparison of the band tensionby a color. For example, green can mean correct band tension, yellowthat the tension measured by the device is within a certain tolerancerange and red that the deviation is too strong, i.e., the tension hasbeen set too tightly or too loosely. The user interface may be displayedon a display device such as a computer, laptop, tablet, or mobile devicefor the medical field.

For the patient, the disclosed procedure can be used to ensure that theligament balancing in the patient's leg after surgery closely matchesthat of the previously recorded reference values. An improvement inrehabilitation of the patient from the operation may result by the useof the measuring instrument to produce the natural kinematics of thepatient, in the ideal case the same muscle tension state of the patientprior to the surgical procedure is restored.

Automatic Logging

A further feature of the disclosed measuring instrument lies in theautomatic recording of the recorded reference values of the patientbefore the start of the operation, as well as the measured values aftersuccessful application of the implant in the patient's joint.Measurement data can be recorded into a program from the measuringdevice and unambiguously assigned to a corresponding patient where therecorded patient-specific measurement and reference values may be storedin an immutable file. The tremendous advantage of this is that in caseof post-surgery issues, a more accurate diagnosis can be made using thepatient-specific data to determine a source of complications. In thelong term, due to the evaluation of this data by the orthopedic surgeoncan result in improved reliability of operations and increase patientsatisfaction. In addition to these advantages, the recording of the datamay also provide legal certainty after operations, both for the surgeon,as well as for the patient, due to accurate logging and unchangeabledocumentation of the values and their traceability through theoperation.

Manufacturer-Independent Measuring Instrument

On the market there are among some big players like the aforementionedcompanies Stryker, Corin, Mathis, and Zimmer Biomet that are in thefield of the manufacture of endoprosthesis. The presently disclosedmeasuring instrument is distinguished by the fact that it is developedin such a way that it may be used independently of the endoprostheticproduct used. A limitation of the applicability and thus the dependencyof one or a few manufacturers of implants for the replacement of kneejoints are thus eliminated and the market for the application is broadlydiversified.

The platform independence of the disclosed device may be achieved via anincision adapter for the femur to the respective prosthesis.

Advantages of one or more of embodiments of the disclosed system andmethod include:

-   -   Objectification and standardization of an operating method,    -   Manufacturer independence,    -   Measurement of the soft tissue tension and the tension profile        of the medial and lateral acting forces over the entire range of        motion of the joint,    -   Easy operation and visually clear display to show deviations        from an ideal state,    -   Production of the patient's natural kinematics,    -   Reduction of the proportion of dissatisfied patients with        problems after the surgery,    -   Faster rehabilitation,    -   Reduced follow-up,    -   Significantly reduced follow-up costs,    -   Recording and logging of the measurement results documentation,    -   Storage in unchangeable file format-traceability for patients        and doctors, and    -   Connection to common hospital software interfaces.

Technical Aspects

Ligament Balancing

An emphasis for the disclosed system and method is to ensure the correctmeasurement of the original tension of the tendons and weighing, as wellas the corresponding transmission of these measured values in theconnection with an artificial knee joint in the patient's leg. Anexisting problem is that measurements for preparing tendon tension onthe opened knee of the patient should not be taken on the “intact” kneesince values obtained with an intact knee are not transferable. Thecorresponding solution disclosed herein includes recording the originaltension condition of the soft parts and tendons in the open state of theknee and transferring the original condition accordingly.

Validation

Closely linked to the previously identified problem of correctmeasurement, is the topic of the validation of the tension historyrecordings of the measurement of the soft tissue tension. Given thenovelty of the disclosed method of operation and production of thecorrect tendon tension using a completely new approach, neitherreference values, nor preliminary studies dealing with of the problemexist. Therefore, performance of detailed examinations and measurementsare disclosed herein.

Material Selection and Sensor Technology

In the area of the right material selection for the manufacture of thedisclosed measurement instrument of tendon tension at the opened knee,the following factors are considered, where according to one embodiment,the measurement instrument (hereinafter referred to as a “ligamentbalancing tool”) may be a “medical disposable product.” A sterilepackaged ligament balancing tool suitable for use in the open knees maybe produced from cost-effective materials. Alternatively, it is possiblefor the tool to be made from completely inert and biologically “safe”materials such as titanium, or gold, for disposable use, albeitcost-intensive. Therefore, in the selection process, a corresponding useis a decisive factor in determining suitable materials for the ligamentbalancing tool. The following points for material selection are from acost-effective point of view.

Biocompatibility of the Material

In terms of biocompatibility, it is important that materials orassemblies used for the ligament balancing tool do not have anynegatives effect on the patient. In particular, for sensors that areembedded within the ligament balancing tool, there are two aspects thatare disclosed in detail herein—the equipment of the sensors in theligament balancing tool, e.g., methods and materials for embedding thesensors to the ligament balancing tool, and the sensors themselves.Capable sensors that are biocompatible and certified for the presentlydisclosed usages are described herewith along with sensor development.

Resistance of the Material-Biological Corrosion

In addition to being safe for the patient when using the material,resistance of the material itself by means of the body or body tissuefluids is of crucial importance. These thematic issues arise especiallywith regard to the consideration of using sensors in the opened knee, aswell as the data transmission required by the sensors to a recordingdevice. The highly corrosive effect of tissue fluids on the formation ofbiotically formed acids or salts, can have a negative effect on theconnections and contacts of sensors. Due to the aggressiveness of thesefluids, rapid progression of corrosion in the sensors and materials usedin the ligament balancing tool is to be expected.

Sensor Technology—Ensuring Measurement Cycles

In addition to the previously mentioned biocompatibility and thestability of the materials against the aggressive environment in thearea of the open knee, that is, the medical fitness of the materialsused, the sensitivity, signal recording, signal interpretation, andsensor position(s) in the ligament balancing tool is of crucialimportance. It is important that the necessary measuring cycles for therecording as well as the setting of the soft tissue tension can beprocessed without appreciable changes in the characteristics of therecording and transmission of the data.

Sterilization

The field of sterilization of tools, are described herein. The preferredway of sterilization of disposable medical devices in industrialsterilization is carried out with ionizing radiation. X-ray radiation,gamma radiation or electron bombardment are predominantly used. Typicalradiation doses that are to be used are in the range of 25 kGy, mostlyfrom gamma radiation from cobalt-60 sources.

Usability for all Standard Implants

A feature of the disclosed ligament balancing tool includes a broadestpossible applicability for nearly all common implants from differentmanufacturers. The success of the disclosed system is ensured byapplicability to at least the implants produced by the largestmanufacturers on the market.

Data Recording, Data Storage

Issues addressed in this section are related to ensuring personal data,the immutability of recorded data, as well as the reading of the datavia the interface.

Interface Issues

The data recorded by the ligament balancing tool can be archivedaccordingly via an interface from the tool to a data acquisition systemconnected to a hospital. In the field of medicine, there areinternationally standardized interfaces for data transfers, but not allhospitals support these interface. Additionally, it is to be consideredwhether there are country-specific or regional regulations are to befollowed.

Personal Data Recording

The disclosed system records sensitive personal data—that is,health-related information, it is ensured that such information is notviewed by unauthorized persons, and a misuse of the personal informationis prevented.

Immutability of Data

Another feature is the immutability of the data recorded by thedisclosed system. Data recorded during the operation, neither duringdata recording, nor transmission of the data to a system of a hospital,in the course of archiving the data in the system, can it be changed. Inthis manner can a complete documentation ensure, in case of a complaintfrom the patient is received, an objective source of information forboth the patient and the surgeon.

Technical Solutions

Ligament Balancing and Validation

A measurement of soft tissue tensions in an open knee, as close aspossible to the original conditions, is described herewith. To getvalidated measurement results, it is important that the tibia isprepared accordingly. A ligament balancing tool may be fitted to thetibial plateau at an angle of 90° to the axis of the tibia. Aftermounting and fixing the tool on the tibial plateau, the soft tissuetension in the leg of the patient stretched from 0° to 90° can bemeasured. The measured values characterized the normal state of the kneeand the values themselves can be validated. If needed, the measurementrange can be extended to a full range of motion.

The ligament balancing tool may comprise a knee endo-prosthetic inlaythat is integrated with sensors to record forces and/or tensions. Theinlay may be produced according to varying sizes of the human knee. Theinlay may be equipped with two or more pressure sensors to record atension profile of both medially and laterally acting forces duringunrolling of the knee in the bended 90° angled position. A referencetension profile can be recorded (measurements may be repeated toeliminate errors) and used for comparison to a final arrangement of theprosthesis in the knee. In this case, the doctor is informed of therange of motion of the leg of the patient, by recording a second tensionprofile after successful implantation of the artificial joint todetermine deviations from the reference profile. A visual display may bepresented via a color bar display where a quick overview (e.g., inrange, out of range) can be represented by a color coding.

According to one embodiment, the inlay may include two or more platformswhere each platform is supported by a scissor arm structure and anunderlying coil spring overlying a sliding surface. One leg of thescissor arm structure may be in a fixed position while a second leg ofthe scissor arm structure is capable of moving along the sliding surfaceupon downward pressure or tension on the platform. Force exerted on theplatform may be transferred to the underlying coil spring where apressure sensor may be positioned below the coil spring to measure adegree of the tension. In a default or initial position, the platformsmay be supported in an up-right position by the springs. After insertingthe inlay in the opened knee, the sliding surfaces are able to bedepressed a given displacement through a 90° range of motion of the leg,which may record the tension produced on the inlay at certain anglesthroughout the range of motion. Measurement may be activated by pressinga start button beginning at the 0° start position of the knee andpressing an end button to confirm reaching an end position (90°) of theknee. Data or signals from the sensors in the inlay may be transmittedby either a wired or wireless communication channel (e.g., Bluetooth) toa computing device over a network.

By evaluating the results in relation to a previously recorded referencetension profile, complex calibration steps in the approval (e.g., fortension forces) of setting soft tissue tension and implant can beavoided. A relatively linear tension profile for the knee in the rangeof 0° to 90° may be expected and any extreme variation may be noted.

Material and Sensor Selection

A special purpose plastic may be envisioned for producing the inlay(including the platforms, scissor arm structure, and sliding surface) asa packaged sterile single-use part. For example, PMFP (polymer medicalflexible plastic), similar to polytetrafluoroethylene (PTFE), has asmooth surface such that foreign substances (e.g., wound secretions) donot adhere to it, and may be used for the inlay. PMFP has highelasticity and temperature resistance and is a biocompatible material.Alternatively, one or more components of the inlay may be high qualitysurgical steel (316L stainless steel), in addition to the coil springs.The sensors may be comprised of biocompatible materials that is capableof temporarily remaining in the body for a short duration of time e.g.,less than 60 minutes. According to one embodiment, the sensors may beencapsulated within the inlays such that the sensors would not be indirect contact with patient tissue.

Sterilization is of the utmost importance to comply with the safety ofthe patient. Sterilization of the instrument may be ensured by selectingappropriate materials for the manufacture of the ligament balancingtool. A preferred method of gamma radiation sterilization, the doses ofradiation in the impact areas are tolerable for most materials, however,having a higher radiation resistance on the outer sides of the productas compared to the product core is advantageous because the doses aresignificantly higher. Especially with plastics, damage can be difficultto avoid because the polymer structure is changed by irradiation. Theconsequences can reduce tensile, breakage, or impact strength of thecomponents. The sterilization process may be taken into account in theconsideration of the design and selection of material for the inlayscomprised in the ligament balancing tool.

Platform independence plays a significant role in the design process ofthe ligament balancing tool. To achieve platform independence,product-specific adapters may be provided to operate the ligamentbalancing tool with products from various global manufacturers of kneeimplants.

Data Recording and Storage

Data may be recorded to a computer program that generates a tensionprofile according to a start and end point. Such data may be processedin a program that supports international data interfaces in the medicalor hospital sector. Additionally, paper prints of the data collected bythe computer program are possible. The data may be tamper-proof andunchangeable according to international standards, thus providing cleartraceability. The computer program may be further coupled to an accesssystem to provide secure access to users by entering a user name andpassword

FIG. 1 presents a ligament balancing tool according to an embodiment ofthe present invention. The ligament balancing tool 100 may comprise aninlay 102 including integrated sensors below each of left platform 104and right platform 106 to measure medial and lateral forces of the kneewhen placed between the tibia and femur bone, and a pin positioningblock 130. Inlay 102 may be produced in different sizes in accordance tovariation in sizes of the human knee. The pin positioning block 130 maybe a detachable component capable of providing a guide for pinpositioning/drilling to assist a surgeon to perform steps required toprepare the femur and tibia for receiving the implant. According to oneembodiment, the ligament balancing tool 100 may be produced as a sterilepackaged single-use part and combined into a product set (e.g.,including a vernier caliper). Additionally, the ligament balancing tool100 may be either platform-dependent (e.g., designed for specificproducts from different manufacturers) or platform independent(universally compatible, e.g., via an adapter).

In one embodiment, the medial and lateral forces may be captured fromthe sensors to create a representative tension profile of the kneeduring 0° to 90° flexion of the knee. The sensors may create voltage orsignals representative of the amount of force or tension produced on theleft platform 104 and right platform 106, individually. Voltage orsignals from the sensors may be coupled to connecting cable 120 fortransmission of the voltage or signals to a computing device via aninterface. The computing device may include software for signalacquisition and processing of the voltage or signals from the sensors toprovide a visualization of the measured data, which is described infurther detail with respect to the description of FIG. 9 and FIG. 10.The computing device may comprise computing devices (e.g., desktopcomputers, terminals, laptops, personal digital assistants (PDA), cellphones, smartphones, tablet computers, or any computing device having acentral processing unit and memory unit capable of connecting to anetwork). The computing device may also comprise a graphical userinterface (GUI) or a browser application provided on a display (e.g.,monitor screen, LCD or LED display, projector, etc.).

Each of left platform 104 and right platform 106 may be supported by ascissor arm structure 112 and 108, respectively, and an underlying coilspring overlying (and attached to inlay 102 at) respective recessedsliding surfaces 116 and 118. A given platform may be supported in anup-right position by an elastic material such as coil spring. Forexample, FIG. 2 presents a right side view of the ligament balancingtool according to an embodiment of the present invention. Right platform106 may be fixed above scissor arm structure 108 and coil spring 110.Pressure may be individually applied to each platform causing theplatforms to move from an extended (or fully upright) position to adepressed position.

FIG. 3 presents a top view of the ligament balancing tool according toan embodiment of the present invention. The ligament balancing tool 100may be placed between the femur and the tibia such that the left andright platforms 104 and 106 are beneath the femur (or femoral component)and inlay 102 is above the tibia (or tibial baseplate). Left platform104 and right platform 106 further includes indentation 130 andindentation 132, respectively. Indentation 130 and 132 may be providedto accommodate the femur bone. The indentations are generally mirrorimages of each other, as shown. Accordingly, the femur bone is able tofit in indentation 130 and 132 without slippage when pressed againstleft and right platforms 104 and 106.

Referring back to FIG. 1, each scissor arm structure may include a fixedleg (122 and 126) that is configured in a fixed position and a slidingleg (124 and 128) that is capable of moving vertically along therecessed sliding surfaces 116 and 118 upon downward pressure or tensionplaced on the left and right platforms (104 and 106). FIG. 4 presents anexposed view of the coil spring 114 and recessed sliding surface 116including fixed leg 122 and sliding leg 124. Pressure applied on leftplatform 104 and right platform 106 may be transferred to pressuresensors beneath coil springs 110 and 114. An additional exposed view andexemplary dimensions of inlay 102 are presented in FIG. 5.

FIG. 6 and FIG. 7 present schematic top view diagrams of the ligamentbalancing tool. Pressure sensors may be positioned below each coilspring to measure a degree of tension. Sensor 202 may be beneath coilspring 114 and sensor 204 may be beneath coil spring 110. In alternativeembodiments, the sensors may be embedded within the coil springs,scissor arm structures, and/or the platforms. Exemplary width of devicefrom sensor 202 to sensor 204 as illustrated is 46.37 mm. Sensors 202and 204 may have of a height of approximately one mm and a diameter ofabout eight mm.

The sensors 202 and 204 may be comprised of pressure or forcemeasurement devices such as piezo or force-sensitive resistor (FSR)sensors that are commercially available. However, capacitive sensors andother strain gauges may also be used accordingly to their durability andreliability. The sensors 202 and 204 may be connected to an electricalor signal bus comprised in connecting cable 120. Connecting cable 120may be adapted from inlay 102 to a connector (e.g., via a wiredconnection) for communication with external electronics that are able toreceive and convert the voltages or signals from sensors 202 and 204into data for display and recording.

FIG. 8 presents an exemplary user interface for displaying data from theligament balancing tool according to an embodiment of the presentinvention. An initiation screen may include fields for patient name 302,patient ID 304, patient number 306 (e.g., an independent patient numberthat can be provided to individual identification systems), kneeidentifier 308, and doctor identifier 310. A size of an inlay may alsobe selected using the inlay identifier 312. Upon population andverification of the data, a user may proceed to measurements byselecting the accept data button 314.

FIG. 9 presents an exemplary user interface for recording a referencetension profile according to an embodiment of the present invention. Thedisclosed ligament balancing tool may transmit measurement signals tosoftware for calculating pressure, angles and distances. A referencetension profile of a “pre-prosthetic” knee may be created and recordedfrom the signals for comparison to a second tension profile, with thefinal assembly of a prosthesis in the knee. The software may beactivated via a start button to start capturing tension data from areference point when the knee is at a 0° position. When the knee hasreached a 90° position, the measuring process may be terminated via anend button.

Signals from the ligament balancing tool may be populated to “pre”medial height 402 and “pre” lateral height 404 measurements on the leftregion of the user interface. The heights may correspond to measureddisplacements of the left and right platforms (e.g., medial and lateralon the left knee) when placed between the femur and tibia during flexionof the knee at reference angles 410. The heights may provide informationabout necessary thickness of bone cuts parallel to the tibial baseplateand in flexion about rotation. Reference angles 410 include angles of0°, 30°, and 60° that may be influenced by distal femoral cuts, and 90°influenced by dorsal cuts (condyles rotation).

Measurements may be repeated on a “post-prosthetic” knee to create thesecond tension profile for comparison with the reference tensionprofile. As illustrated in FIG. 10, measurement signals from theligament balancing tool may be populated to “post” medial height 406 and“post” lateral height 408 for reference angles 410 on the right regionof the user interface. The “pre” and “post” measurements at thereference angles 410 may be compared to determine a degree of differencebetween the tension profiles. By comparing the “pre” and “post”measurements, a surgeon may be able to determine or adjust medial andlateral heights for the knee to achieve appropriate stability andtension state. According to the illustrated example, each box inreference angles 410 may be shaded in a color that corresponds to anindication of “in-range” and “out-of-range” knee angles after “post” oroperation incisions.” A knee is preferably operated such that the lengthbetween the medial and lateral distance is within a certain range toavoid instability and pain. For example, green may be shown to indicatethat there is not more than a three mm difference between the medial andlateral heights. Yellow may indicate that there is more than a three mmdifference between the medial and lateral heights which may beborderline acceptable depending on general condition and anatomicalcondition, and recuts may be necessary according to the measuredresults. Red may indicate that there is more than five mm differencebetween the medial and lateral heights which may be out of a requiredrange, and recuts are necessary. Accordingly, reference angles 410 mayindicate certain knee angles that require recuts and an amount to recutbased on the color indications.

FIG. 11-14 present views of a ligament balancing tool according to analternative embodiment of the present invention. FIG. 11 shows aligament balancing tool 1100 comprising an inlay 1102 that includes aleft platform 1104 and a right platform 1106. Referring to FIG. 12, leftplatform 1104 is attached to scissor arm structure 1108 which iscomprised of a fixed leg 1122 and a sliding leg 1124. Right platform1106 is attached to scissor arm structure 1112 which is comprised of afixed leg 1126 and a sliding leg 1128. Referring back to FIG. 11, fixedleg 1122 and sliding leg 1124 are attached to inlay 1102 at recessedsliding surface 1116, and similarly, fixed leg 1126 and sliding leg 1128are attached to inlay 1102 at recessed sliding surface 1118. The slidinglegs (1124 and 1128) are capable of moving vertically along the recessedsliding surfaces 1116 and 1118 upon downward pressure or tension placedon the left platform 1104 and right platform 1106.

FIG. 12 further illustrates left platform 1104 and right platform 1106positioned above coil spring device 1110 and coil spring device 1114.Force sensing sensors may be placed underneath coil spring device 1110and coil spring device 1114. For example, FIG. 13 presents a right-sidecross-sectional view of ligament balancing tool 1100 where coil springdevice 1110 is positioned above sensor 1130 such that coil spring device1110 makes contact (direct or indirect) with sensor 1130 when rightplatform 1106 is depressed. Inlay 1102 further includes a cable 1120that is electronically connected to the sensors beneath coil springdevice 1110 and coil spring device 1114 for transmission of signals ordata from the sensors (associated with a tension, pressure, ordisplacement applied to left platform 1104 and right platform 1106) to acomputing device. FIG. 14 presents a bottom view of the ligamentbalancing tool where inlay 102 further includes a sensor cover 1132.Sensor cover 1132 may be placed over circuitry associated the sensorsand cable 1120.

FIGS. 1 through 14 are conceptual illustrations allowing for anexplanation of the present invention. Notably, the figures and examplesabove are not meant to limit the scope of the present invention to asingle embodiment, as other embodiments are possible by way ofinterchange of some or all of the described or illustrated elements.Moreover, where certain elements of the present invention can bepartially or fully implemented using known components, only thoseportions of such known components that are necessary for anunderstanding of the present invention are described, and detaileddescriptions of other portions of such known components are omitted soas not to obscure the invention. In the present specification, anembodiment showing a singular component should not necessarily belimited to other embodiments including a plurality of the samecomponent, and vice-versa, unless explicitly stated otherwise herein.Moreover, applicants do not intend for any term in the specification orclaims to be ascribed an uncommon or special meaning unless explicitlyset forth as such. Further, the present invention encompasses presentand future known equivalents to the known components referred to hereinby way of illustration.

It should be understood that various aspects of the embodiments of thepresent invention could be implemented in hardware, firmware, software,or combinations thereof. In such embodiments, the various componentsand/or steps would be implemented in hardware, firmware, and/or softwareto perform the functions of the present invention. That is, the samepiece of hardware, firmware, or module of software could perform one ormore of the illustrated blocks (e.g., components or steps). In softwareimplementations, computer software (e.g., programs or otherinstructions) and/or data is stored on a machine readable medium as partof a computer program product, and is loaded into a computer system orother device or machine via a removable storage drive, hard drive, orcommunications interface. Computer programs (also called computercontrol logic or computer readable program code) are stored in a mainand/or secondary memory, and executed by one or more processors(controllers, or the like) to cause the one or more processors toperform the functions of the invention as described herein. In thisdocument, the terms “machine readable medium,” “computer readablemedium,” “computer program medium,” and “computer usable medium” areused to generally refer to media such as a random access memory (RAM); aread only memory (ROM); a removable storage unit (e.g., a magnetic oroptical disc, flash memory device, or the like); a hard disk; or thelike.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the relevant art(s) (including thecontents of the documents cited and incorporated by reference herein),readily modify and/or adapt for various applications such specificembodiments, without undue experimentation, without departing from thegeneral concept of the present invention. Such adaptations andmodifications are therefore intended to be within the meaning and rangeof equivalents of the disclosed embodiments, based on the teaching andguidance presented herein. It is to be understood that the phraseologyor terminology herein is for the purpose of description and not oflimitation, such that the terminology or phraseology of the presentspecification is to be interpreted by the skilled artisan in light ofthe teachings and guidance presented herein, in combination with theknowledge of one skilled in the relevant art(s).

What is claimed is:
 1. A system for measuring tension, pressure anddistance of joint tissue, the system comprising: a prosthetic inlaydevice comprising: at least two platform structures, wherein each of theplatforms are supported on a scissor arm structure and a spring, andwherein each of the platforms are configured to variably depress thespring through a range of motion of a joint when the prosthetic inlaydevice is placed in situ; a force sensing sensor configured beneath eachspring, the force sensing sensor detecting pressures from depressing thespring at each of the at least two platform structures; and acommunication interface coupled to the force sensing sensors, thecommunication interface transmitting data corresponding to the detectedpressures to a computing device that is configured to generate a set ofheights representing displacement of the at least two platformstructures and corresponding to medial and lateral tension on the jointtissue based on the detected pressures at a plurality of referenceangles of the joint.
 2. The system of claim 1 further comprising asliding surface beneath the scissor arm structures.
 3. The system ofclaim 2 wherein the scissor arm structure includes a fixed leg and asliding leg.
 4. The system of claim 3 wherein the sliding leg isoperable to move along the sliding surface.
 5. The system of claim 1wherein the at least two platform structures include indentationsconfigured to conform to a patient's femur.
 6. The system of claim 1wherein the prosthetic inlay device comprises biocompatible material. 7.The system of claim 1, wherein the set of heights comprises a first setof heights representing displacement of the at least two platformspre-prosthesis and a second set of heights representing displacement ofthe at least two platforms post-prosthesis.
 8. The system of claim 7,the computing device further configured to determine differences betweenthe first and second sets of heights and display an indication for oneor more of the plurality of reference angles of the joint.
 9. A method,in a data processing system comprising a processor and a memory, formeasuring tension, pressure, and distance of knee tissue, the methodcomprising: receiving, by a computing device, a first set of signalsfrom a ligament balancing device including at least two platformstructures, wherein each of the platform structures are supported on ascissor arm structure and a spring, and force sensing sensors thatmeasure force applied to each of the at least two platform structuresthat variably displace each of the springs through a range of motion ofa knee when the ligament balancing device is placed in situ, the firstset of signals representative of force applied to each of the at leasttwo platform structures by a femur at one or more knee flexion anglesprior to a prosthetic operation; identifying, by the computing device, afirst set of medial and lateral forces at the one or more knee flexionangles from the first set of signals; receiving, by the computingdevice, a second set of signals from the ligament balancing device, thesecond set of signals representative of force applied to each of the atleast two platform structures by the femur at the one or more kneeflexion angles subsequent to the prosthetic operation; identifying, bythe computing device, a second set of medial and lateral forces at theone or more knee flexion angles from the second set of signals;determining, by the computing device, a first set of heights representdisplacement of the at least two platforms structures based on the firstset of medial and lateral forces and a second set of heights correspondto displacement of the at least two platforms based on and the secondset of medial and lateral forces; determining, by the computing device,an amount of difference between the first set of heights and the secondset of heights at each of the one or more knee flexion angles; anddisplaying, by the computing device, an indication for the one or moreknee flexion angles based on the determined amount of difference betweenthe first set of heights and the second set of heights.
 10. The methodof claim 9, wherein the first set of heights are determinedpre-prosthesis and the second set of heights are determined postprosthesis.